chemical reactions of group 3 elements with water, oxygen and chlorine
Answers
Answer:
Sodium
Sodium has a very exothermic reaction with cold water producing hydrogen and a colourless solution of sodium hydroxide.
Magnesium
Magnesium has a very slight reaction with cold water, but burns in steam.
A very clean coil of magnesium dropped into cold water eventually gets covered in small bubbles of hydrogen which float it to the surface. Magnesium hydroxide is formed as a very thin layer on the magnesium and this tends to stop the reaction.
Magnesium burns in steam with its typical white flame to produce white magnesium oxide and hydrogen.
Aluminium
Aluminium powder heated in steam produces hydrogen and aluminium oxide. The reaction is relatively slow because of the existing strong aluminium oxide layer on the metal, and the build-up of even more oxide during the reaction.
Silicon
There is a fair amount of disagreement in the books and on the web about what silicon does with water or steam. The truth seems to depend on the precise form of silicon you are using.
The common shiny grey lumps of silicon with a rather metal-like appearance are fairly unreactive. Most sources suggest that this form of silicon will react with steam at red heat to produce silicon dioxide and hydrogen.
But it is also possible to make much more reactive forms of silicon which will react with cold water to give the same products.
Note: These more reactive forms are produced as powders. Cotton and Wilkinson's Advanced Inorganic Chemistry (third edition - page 316) suggests that the reactivity of one of these could be due to a very high surface area, or perhaps because the silicon exists in a graphite-like structure.
A correspondent from the silicon industry tells me that when silicon is cut into slices, the silicon dust formed reacts with water at room temperature - producing hydrogen and getting very hot. He says
"The silicon is cut in a glycol slurry [. . .] The powdered Si is protected somewhat from moisture in the glycol slurry, but when we clean the slurry in aqueous solutions the reaction with water takes off."
This is probably the effect of the high surface area of the dust produced, combined with the fact that you are exposing uncontaminated silicon to the water. One source suggests that the lack of reactivity of silicon is due to a layer of silicon dioxide on its surface. If you expose a new surface by cutting the silicon, that layer won't, of course, exist.
Phosphorus and sulphur
These have no reaction with water.
Chlorine
Chlorine dissolves in water to some extent to give a green solution. A reversible reaction takes place to produce a mixture of hydrochloric acid and chloric(I) acid (hypochlorous acid).
Note: You may also find the chloric(I) acid written as HClO. The form I have used more accurately reflects the way the atoms are joined up. It doesn't matter which you use.
In the presence of sunlight, the chloric(I) acid slowly decomposes to produce more hydrochloric acid, releasing oxygen gas, and you may come across an equation showing the overall change:
Chemical reactions of group 3 elements with water:
Sodium(Na) reacts vigorously with water to give the hydroxide and hydrogen:
2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
The resulting solution is strongly alkaline and will have a pH of 14.
Magnesium(Mg) reacts with cold water very slowly, but can react quickly with steam to give the oxide and hydrogen:
Mg(s) + H2O(g) → MgO(s) + H2(g)
The resulting solution is weakly alkaline since the oxide is slightly basic (pH = 9).
Aluminum(Al) reacts with water to produce hydrogen gas according to the equation:
2Al + 3H2O → 3H2 + Al2O3.
Silicone(Si): Water and water vapor probably have little influence upon silicon solubility, because a protective surface layer of silicon dioxide is rapidly formed. There are many examples of silicon compounds reacting with water. Silicon tetrafluoride reacts with water to hydrogen fluoride. Silicon tetrachloride reacts with water quite violently. Silicides of the first and second groups are generally more reactive than transitory metals. Typical reaction products include hydrogen and silanes (SiH4), for example
Na2Si + 3H2O → Na2SiO3 + 3H2.
Chemical reactions of group 3 elements with oxygen:
Sodium(Na)
4Na(s) + O2(g) → 2Na2O(s)
Na2O is an ionic oxide. This reaction is very vigorous as sodium burns with a yellow flame
Magnesium(Mg)
2Mg(s) + O2(g) → 2MgO(s)
MgO is also an ionic oxide. This reaction is vigorous with a brilliant white flame forming white ash of magnesium oxide.
Aluminum(Al)
4Al(s) + 3O2(g) → 2Al2O3(s)
Al2O3 is mostly ionic, but there is a significant covalent character. This reaction is initially vigorous.
Silicone(Si)
Si(s) + O2(g) → SiO2(s)
SiO2 is a giant covalent oxide. This reaction is slow.
Chemical reactions of group 3 elements with chlorine:
Sodium(Na)
2Na(s) + Cl2(g) → 2NaCl(s)
NaCl is an ionic chloride. This is a very vigorous reaction.
Magnesium(Mg)
Mg(s) + Cl2(g) → MgCl2(s)
MgCl2 is also an ionic chloride. Vigorous reaction when the elements are heated.
Aluminum(Al)
2Al(s) + 3Cl2(g) → 2AlCl3(s)
AlCl3 is covalent. It forms a polymeric structure in the solid-state, turning quickly on heating into a dimeric gas (Al2Cl6). It thus behaves as a simple molecular chloride. This reaction is vigorous when the elements are heated under anhydrous conditions.
Silicone(Si)
Si(s) + 2Cl2(g) → SiCl4(s)
SiCl4 is a molecular covalent chloride. Slow reaction.
Phosphorous(P)
P4(s) + 10Cl2(g) → 4PCl5(s)
This is a slow reaction. P2Cl10 is actually ionic in the solid-state - it exists as [PCl4]+[PCl6]- in the solid-state.